1. Field of the Invention
The present invention relates generally to pumping of natural resources from below ground to the surface and more specifically to devices to protect and improve the efficiency of pumps used for such purposes.
2. Background Information
In the United States and throughout the world, a variety of natural resources including oil, water, and methane (a natural gas), are found beneath the earth""s surface and brought to the surface through a variety of wells. In some instances these resources are under pressure and will naturally flow through the well to the surface without application of other means. In other cases, a pump which has much of its components on the surface is used to pump the resource from the ground. In some instances, a pump, often a submersible pump, is placed beneath the surface in a production zone within or near the source of the resource.
In most cases in which an underground pump is used, a hole is drilled from the surface to the production zone and a pipe of some type is inserted into the hole between the surface and the production zone. The well is often xe2x80x9ccasedxe2x80x9d by forcing concrete into the area between the outer surface of the pipe and the surface of the hole. The area near the production zone (the area within or near the source of the resource) is usually below the pipe and casing or placed in communication with the inside of the pipe or pipe and casing by the inclusion of holes in the pipe and/or casing. If an underground pump is used, the pump is suspended beneath the surface in the production zone.
The extraction of methane from coal deposits in many western states provides a good example of a well which uses an underground pump. The methane gas is entrained in water which permeates porous and permeable layers of coal found beneath the surface. A hole is drilled from the surface to the top of the coal deposit. The hole is cased with pipe from the surface to the top of the coal deposit. The production zone is a hole within the coal and is open to the cased area. A delivery pipe runs within the cased pipe from the surface to the production area and a submersible pump is affixed to the underground end of the delivery pipe. Ordinarily, water and methane will seep from the coal into the hole around the pump. The water and a small amount of methane are pumped through the delivery pipe to the surface where the water and methane are separated. Most of the methane flows up the cased hole outside the delivery pipe and is then removed and processed. The removal of water and methane from the production zone causes a pressure differential between the area close to the pump and outlying areas which tends to cause the water and methane to flow from the coal to the production zone near the pump.
A number of conventional submersible pumps may be used for this purpose and nearly all of them have a screened intake port through which the water enters the pump body. The water drawn into the pump also includes fine coal particles and other solid matter. Usually, after a period of operation, the solid particles (including coal particles) clog the pump""s intake port and, more importantly, the pump impellers within the pump. Such clogging causes a variety of problems. The most obvious problem arising from clogging is that the extraction of water stops and methane production falls off dramatically or ceases, because there is no longer a pressure differential between the production zone and the surrounding area of the coal deposit. In addition, if the pump continues to operate with little or no flow of water, the pump will overheat and eventually fail. In many cases where the pump""s intake port or pump impellers are clogged, the pump must be retrieved from the hole and cleaned. In cases where the pump fails or is damaged, the pump must be retrieved and either replaced or repaired. Often a system of sensors and controls are employed which sense that the intake port is clogged and the pump is laboring and the pump is automatically shut off.
Another significant problem which arises with the use of submersible pumps is overheating.
Another problem in coal bed methane production is associated with wells which are particularly xe2x80x9cgassy.xe2x80x9d That is, significant amounts of methane are pumped up through the delivery pipe with the water and do not flow up the well outside of the delivery pipe. In most cases this results in significant amounts of methane being lost.
Another problem associated with submersible pumps, especially higher horsepower pumps, is pump failure caused by what is known as xe2x80x9cupthrust.xe2x80x9d Most submersible pumps are manufactured as a series of stages stacked within a cylindrical case. Each stage includes an impeller and all of the impellers are usually powered by a single electric motor. When the pump is started up, the first stage impels the liquid up into the second stage and then the first and second stages impel the liquid up into the third stage. This process continues until all the stages are engaged and the liquid is forced out of the pump. As each stage is engaged, it adds its pumping force to the force provided by the previous stages. At startup, this combination of the upward force imparted by the lower stages of the pump or upthrust causes considerable wear and fatigue upon the elements of the upper stages of the pump. In some cases, a pump will even fail immediately upon startup because the upthrust of the lower stages of the pump cause failure of one or more of the upper stages.
The invention presented in the present application is believed to solve, in a simple and effective fashion, problems which have long plagued persons engaged in pumping resources from a well with a submersible pump: a pump protection system which provides a screen between the production zone and the pump intake port to prevent unwanted solids from reaching and clogging the pump intake port, which provides a method of cleaning such solids from the screen without removing the pump protection system or the pump from the production zone, which acts to eliminate or greatly reduce entrained gases from moving with the pumped fluid through the delivery pipe, which acts to prevent overheating, and which prevents pump failure due to upthrust at startup.
Although the pump protection system of the instant invention may be used in a variety of situations for extraction of a variety of resources, the following example is based upon the extraction of methane and water from underground coal seams, such methane is often described as xe2x80x9ccoal bed methane.xe2x80x9d The well is as described above. The pump protection system of the instant invention is attached to the delivery pipe near the bottom of the delivery pipe and completely surrounds the pump. The water from the production zone must pass through a protection system screen before it enters the intake port of the pump. If the protection system screen becomes clogged, a self-cleaning method is provided such that the system may be back-flushed and particles removed from the protection system screen with no reverse flow through the pump. The pump protection system of the instant inventions solves problems related to overheating by preventing clogging in a manner which also provides for a flow of cooling fluid around of the pump motor. The configuration of the pump protection system and the flow path of water within the pump protection system also helps to prevent methane from flowing with the water through the delivery pipe. The pump protection system of the instant invention also includes a pressure relief valve which acts to prevent upthrust damage at pump startup.
The ideal pump protection system should screen unwanted solid particles from reaching the intake port of the pump and clogging the intake port or jamming or causing excessive wear of the internal pump impellers. The ideal pump protection system should also provide a self-cleaning method whereby solid particles which collect upon the protection system screen may be flushed from the protection system screen without retrieving the pump or pump protection system from the production zone and without back flow through the pump. The ideal pump protection system should also help to prevent overheating of the pump and pump motor. The ideal pump protection system should also act to prevent gases from being pumped with the water through the delivery pipe. The ideal pump protection system should also include a method of preventing upthrust damage to the involved pump. The ideal pump protection system should also be simple, rugged, inexpensive, and easy to use.
In situations in which liquid or gaseous resources are pumped from beneath the ground to the surface, the present invention provides a pump protection system which screens unwanted solid particles from the pump intake port and prevents them from clogging the pump intake port or from jamming the pump""s internal impellers. The production zone is the area around the pump intake port and the pump protection system may be employed in situations in which the entire pump (with intake port) is in or near the productions zone or in which the intake port is in the production zone and at least part of the pump is at the surface or otherwise outside the production zone.
Although the pump protection system of the instant invention may be used in a variety of situations, the following example is based upon the pumping of water and extraction of methane from a coal seam as described above. A typical well has an enclosed portion between the surface and a position near the top of the production zone. The well is open and in communication with the water and methane bearing coal at and near the production zone. A delivery pipe runs from the surface within the enclosed portion of the well to the production zone. A top valve flange is affixed to the lower end of the delivery pipe. The outflow port of a pump is affixed to a bottom valve flange and the bottom valve flange is connected to the top valve flange. A valve is seated between the top valve flange and the bottom valve flange. The top valve flange, bottom valve flange, and the valve make up a valve assembly.
The outer portion of the pump protection system, the shell, includes an upper seal cap at its top, a middle body portion, and a lower cap. The upper seal cap fits around the delivery pipe just above the top valve flange and forms a waterproof seal around the delivery pipe. The body of the pump protection system completely surrounds and encloses the valve assembly and the pump, and, thus, the pump intake port. The lower cap closes the bottom of the body and serves to center the assembly during insertion into the production zone. The lower portion of the body of the pump protection system is composed of a screen with a mesh sufficiently fine to allow water to enter the shell, but to prevent nearly all entrained coal particles, and other unwanted solid particles from entering the shell. The pump protection system is also designed so that methane which is entrained in the water entering the protection system flows back out of the protection system and up the well outside the delivery pipe.
The valve assembly may also include a pressure relief valve which acts to prevent upthrust damage to the pump. It is well known that back pressure greatly reduces or eliminates pump damage caused by upthrust. That is, a sufficient amount of downward pressure upon the upper stages of a pump counteracts and eliminates or greatly reduces the upthrust damage caused to the upper stages of a pump by the upward force of the lower stages. For example, after a pump has been in operation for a while, the downward force of the column of water above the pump is usually sufficient to counteract the upthrust and greatly reduces or eliminates the upthrust damage to the upper pump stages. In most cases, the amount of downward pressure sufficient to counter upthrust damage is known. As another example, a column of water in the delivery pipe 170 feet high might provide sufficient back pressure with a ten horsepower submersible pump to counteract the negative affects upon the pump of pump upthrust. In this example, the pressure relief valve would allow the system to back flush to clean the screen as long as the column of water in the delivery pipe was greater that 170 and would stop the flow of water back through the pump protection system when the column reached the height of 170 feet. Therefore, when the pump was restarted, upthrust damage would be reduced or eliminated because the back pressure of the 170 foot column of water on the upper stages of the pump would be sufficient to counteract the upthrust of the lower pump stages. At initial startup, upthrust damage could be curtailed by the simple expedient of filling the delivery pipe with water and allowing the water level to reach the 170 foot depth automatically because of the pressure relief valve.
In operation, the pump pumps water from the production zone up to the surface through the delivery pipe. The water and methane from the production zone are collected, separated, and cleaned in processes which are not considered part of the instant invention. The removal of water and methane from the production zone near the pump causes a pressure differential which, in turn, causes additional water and methane to flow from outlying areas into the production zone. In this pumping mode, the valve opens in a manner which allows the water to flow through the pump outflow port and up the delivery pipe. The water flows into the shell through the screen which catches solid particles and prevents them from entering the pump intake port. The pump protection system is designed such that relatively high velocity water flows around the pump motor and provides a cooling effect. Various methods, including monitoring the amount of current the pump is drawing, may be used to determine whether the screen has become sufficiently clogged to prevent appropriate amounts of water from flowing through the screen and into the shell. At this point the pump is shut off leaving a significant column of standing water within the delivery pipe above the pump. The valve is designed such that it is open between the pump outflow port and the delivery pipe when the pump is pumping water, but is closed between the outflow port and the delivery pipe when the pump is shut off. When this pumping path is closed, the valve automatically opens a second path, the cleaning path, which places the column of water within the delivery pipe into communication with the inside of the shell outside of the pump. The pressure head in the column of water is greater than the pressure from the water in the productions zone, and the water within the delivery pipe flows downward through the delivery pipe, through the shell, and out of the shell through the screen. This reverse flow of water or back flush acts to clean the screen. The operator may restart the pump and resume operations at any time during the gravity back flush.
The pressure relief valve portion of the valve assembly is open during the above described back flush operation as long as the column of water within the delivery pipe is higher than is sufficient to counteract upthrust damage and allows water to flow in the path described above to clean the screen. However, once the column of water reaches the level necessary to counteract upthrust, the pressure relief valve acts to close the water flow path through the pump protection system and prevents further back flush flow.
A flow tube within the shell projects downward below the pump to a position close to but above the bottom of the shell. Thus, when the pump is in pumping mode, the flow of water into the shell is in through the screen, downward toward the bottom of the shell, and then upward to the pump intake port. Although most of the methane does not pass through the screen, some enters through the screen with the water. This flow path causes much of the methane which enters through the screen into the shell to bubble up outside the flow tube and out through the screen near the top of the screen. This methane then flows outside the delivery pipe to the surface and does not flow with the water up through the delivery pipe. This greatly reduces the problems associated with surging current and torque and methane loss in gassy wells as described above.
Although the above summary relates to extraction of water and methane from a coal seam, the instant invention could be used in a number of situations where a liquid containing solid particles which could clog a pump intake port is pumped from underground to the surface. The pump protection system could even be used in situations in which the pump was located entirely above ground as long as there was some form of pump intake port beneath the surface.
One of the major objects of the present invention is to provide a pump protection system which screens unwanted solid particles from reaching the intake port of the pump and clogging the intake port and from jamming internal pump impellers and from causing excessive wear.
Another objective of the present invention is to provide a self-cleaning method whereby solid particles which collect upon the protection system screen may be flushed from the protection system screen without retrieving the pump or pump protection system from the production zone.
Another objective of the present invention is to help to prevent overheating of the pump motor.
Another objective of the present invention is to provide a pump protection system which prevents methane entrained in the water entering the pump protection system from flowing through the pump.
Another objective of the present invention is to reduce or eliminate upthrust damage by maintaining sufficient back pressure within the delivery pipe at the pump discharge to counteract upthrust damage.
Another objective of the present invention is to provide a pump protection system which is simple, rugged, inexpensive, and easy to use.
These and other features of the invention will become apparent when taken in consideration with the following detailed description and the drawings.